Pretty cool. Back to the Future 2 was always innovative in the way it sent the main story against the original film. i stumbled across this video where the two intersecting segments at the dance are synced and overlapped in split screen.

nah. the more I think about it, the more I think it needs to be done similar to the way it was in the link: one independent (prespliced) stream. I was originally thinking you could use the pop-up screen on the BACK TO THE FUTURE 2 disc, but for one thing, you'd still need to stop/start the main movie to synch it with the extra content of the first. I suppose they could create an alternate pcg and give you some kind of overlay option like in HOLY GRAIL or MATRIX dvds that would kick you out of the main feature: run the alternate content, then insert you into the main feature at a later point than you left.